Sinatra before 2.0.2 has XSS via the 400 Bad Request page that occurs upon a params parser exception.
{ "nvd_published_at": "2018-05-31T19:29:00Z", "cwe_ids": [ "CWE-79" ], "severity": "MODERATE", "github_reviewed": true, "github_reviewed_at": "2020-06-16T21:46:50Z" }